TWI622491B - Hot stamping forming low heat transfer heating mold and hot stamping part forming method - Google Patents

Abstract

A low-heat transfer heating mold and a hot stamping part forming method for hot stamping forming, wherein the heating mold structure comprises: a concave mold and a convex mold which are correspondingly combined with each other, and the concave mold has a first working area contacting the billet The convex mold has a second working area contacting the billet; a low heat transfer layer coated on the first working area and/or the second working area; and the hot stamping forming method step comprises: moving an Oswego ironizing temperature Forming the steel plate to a low heat transfer heating mold; quenching the formed steel plate in a low heat transfer heating mold at a cooling rate of 25 ° C / sec. or less to form a metallographic structure of the ferrite iron with the contact zone of the formed steel sheet and the low heat transfer layer Mainly low intensity areas.

Description

Hot stamping forming low heat transfer heating mold and hot stamping part forming method

The present invention relates to a hot stamping hot stamping die and a hot stamping die forming method, and more particularly to a heating die and a hot stamping die forming method having a low heat transfer surface in contact with a workpiece.

Hot stamping is the mainstream technology of high-strength steel process, which can obtain ultra-high strength body parts, reduce the thickness of parts, reduce the number of body reinforcement plates, improve the collision performance of the body and effectively reduce weight. The forming property is good, the complex shape piece can be formed, the elasticity of the design can be improved, and the comprehensive manufacturing cost can be effectively controlled. Since the steel plate must be subjected to the in-mold quenching process immediately after the high-temperature forming, the mold temperature will affect the microstructure change after the steel plate is quenched. Therefore, the control of the cooling temperature will be a major issue, and the hot stamping die has the dual functions of forming and quenching, and is an important equipment for hot stamping forming technology.

US Patent No. 20120097298 A1 discloses a method of manufacturing a partially hardened steel member, the body of which consists of a hardenable steel sheet, subjected to elevated temperatures sufficient to quench harden, after reaching the desired temperature, and optionally at the desired After the holding time, the embryo body is transferred to a molding tool, in which the body body is formed and hardened at the same time, or the body is cold-formed, and then the molded article obtained by cold forming is heated. The heating is carried out such that the molding temperature required for quench hardening is reached, and the molded part is then transferred to a tool in which the heated molded part is cooled and hardened by quenching, characterized in that During the heating of the body or molded part by the temperature rising to the temperature required for hardening, the absorbent material rests on and/or has a small gap between the areas which tend to have lower hardness and/or higher ductility. From the aspect of expansion and thickness, thermal conductivity, heat capacity, and/or emissivity of the absorbing material It is considered that the absorbing material is sized such that thermal energy acting in the region of the molded part to be maintained in ductility flows into the absorbing material through the molded part. However, the technique needs to consider how the heat absorbing material is indeed placed on the body or component without falling off, and cannot be detached during the heating process, and after the quenching and hardening is completed, the heat absorbing material needs to be moved from the finished product. In addition, many additional processes are derived.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a low thermal conductivity surface in the area where a hot stamping die is in contact with a hot stamped workpiece to improve the cooling profile control capability to achieve a lower strength in the same product.

In order to achieve the above structure, the present invention provides a low-heat transfer heating mold for hot stamping, comprising: a set of concave and convex molds and a low heat transfer layer disposed on the concave and convex mold. The concave mold has a first working area contacting the blank, and the convex mold has a second working area contacting the blank; the low heat transfer layer is coated on the first working area and/or the second working area.

In one embodiment, the low thermal transfer coating is applied to all or a portion of the first working area and/or the second working area.

In one embodiment, the low thermal transfer coating is a ceramic coating.

In one embodiment, the low thermal transfer layer is plated in the first working area and/or the second working area by plasma spraying (the first working area and/or before plating the low thermal transfer layer) The surface of the second working area may be further subjected to a roughening treatment).

In order to achieve the above-described method for forming a hot stamping part, the present invention provides the steps of: moving a formed steel sheet uniformly heated to the rolling temperature of Austin to the aforementioned low heat transfer heating mold; and subjecting the formed steel sheet to the low heat transfer The heated mold is quenched and has a cooling rate of about 25 ° C / sec. or less.

In one embodiment, the low heat transfer heated mold has a temperature greater than 420 ° C and a quenching time greater than 80 seconds.

In one embodiment, the moving time of the formed steel sheet to the low heat transfer heating mold is 10 seconds, and the heating temperature of the low heat transfer heating mold is 450 ° C, and the quenching time is 100. In seconds, the air cooling time is 120 seconds.

The invention has the following features: the invention provides a mold with excellent cooling curve control capability, and can have the advantages of working at a low heating mold temperature, and can save part of heating energy; the invention can produce hot stamping process with different strengths of the same part The invention combines the heating of the mold and the low heat conduction coating structure design on the surface of the mold, and can further reduce the quenching effect/strength of the hot stamped steel sheet without relying on special equipment and shortening the cycle time.

1‧‧‧Low heat transfer heating mould

11‧‧‧ concave die

111‧‧‧Mold face

1111‧‧‧First work area

12‧‧‧ Punch

121‧‧‧Mold face

1211‧‧‧Second work area

13‧‧‧Low heat transfer coating

131‧‧‧Down mold low heat transfer coating

132‧‧‧ Punch low heat transfer coating

20‧‧‧Bulette

C‧‧‧ standard curve

T1‧‧‧ first experimental test piece

T2‧‧‧Second experimental test piece

T3‧‧‧ third experimental test piece

T1, t2, t3‧‧‧ continuous cooling curve

Step S10 to Step S12‧‧‧ Forming Step of Forming Method of Hot Stamping Parts

Step S13‧‧‧forming steps in combination with air-cooled cooling means

1 is a schematic perspective view of a low heat transfer heating mold of the present invention; FIG. 2 is a front view of the low heat transfer heating mold stamping blank; FIG. 3 is a front view of the low heat transfer heating mold stamping blank of the present invention; Figure 4 is a flow chart showing the steps of forming a hot stamping part of a low heat transfer heating mold according to the present invention; Fig. 5 is a continuous cooling curve of each embodiment of the hot stamping part forming method of the low heat transfer heating mold of the present invention; Figure.

The present invention is described in detail below with reference to the drawings, and the drawings are simplified schematic diagrams, and the basic structure of the present invention is only illustrated in a schematic manner, and therefore only the components related to the present creation are indicated in the drawings. The components shown are not drawn in the number, shape, size ratio, etc. at the time of implementation, and the actual size of the implementation is a selective design, and the component layout form may be more complicated.

Please refer to FIG. 1, FIG. 2 and FIG. 3 at the same time. The low-heat-transfer heating mold 1 of the hot stamping of the present embodiment includes: a die 11 and a punch 12 in which a plurality of mold faces (111, 121) are coupled to each other, and low heat on the die 11 and the punch 12 a transfer layer 13 having a first working area 1111 contacting the billet 20, the punch 12 having a second working area 1211 contacting the billet 20, the low heat transfer layer 13 comprising the first work The recessed low heat transfer layer 131 and/or the punch low heat transfer layer 132 of the region 1111 and/or the second working region 1211.

In an embodiment, the low thermal transfer layer 13 is coated on all or part of the first working area 1111 and/or the second working area 1211.

In an embodiment, the low thermal transfer layer 13 can be a ceramic coating.

In one embodiment, the low thermal transfer layer 13 has a thickness of 0.3 mm, a melting point of about 2000 ° C, a thermal conductivity of 2.2-2.9 (W/mK), and a thermal expansion coefficient of 11 x 10 ^-6 (1/K).

In one embodiment, the low heat transfer layer 13 is plated in the first working area 1111 and/or the second working area 1211 by plasma spray, and the low heat transfer layer 13 is plated. Previously, the surface of the first working area 1111 and/or the second working area 1211 may be preliminarily subjected to a roughening treatment to improve the bonding strength of the low heat transfer layer 13.

Continued see Figure 4. The step of forming the hot stamping member of the present embodiment includes the step S10 of providing the low heat transfer heating mold 1 of any of the foregoing embodiments. Step S11, moving a formed steel sheet (ie, billet 20) uniformly heated to the rolling temperature of Austin to the low heat transfer heating mold 1 for hot stamping; and step S12, heating the formed steel sheet (binder 20) The low heat transfer heating mold 1 is quenched in a cooling rate of less than 25 ° C / sec.; thereby, the contact area of the formed steel sheet (binder 20) with the low heat transfer layer 13 is formed into a gold The phase-based low-strength region, and the portion of the formed steel sheet (the billet 20) that is not in contact with the low-heat transfer layer 13 contains a high-strength region of the original stamping.

In an embodiment, after the quenching process in the heating mold 1 for completing the low heat transfer (step S12), the method further comprises: step S13, moving the formed steel sheet (the billet 20) out of the low heat transfer heating mold 1 and Cool in air for 120 seconds.

In an embodiment of the method of forming a hot stamping, the low heat transfer heated mold has a temperature greater than 420 ° C and a quenching time greater than 80 seconds.

In an embodiment of the forming method of the hot stamping part, the moving time of the formed steel sheet (binder 20) moved to the low heat transfer heating mold is 10 seconds, and the heating temperature of the low heat transfer heating mold is 450 ° C, quenching The time is 100 seconds and the air cooling time is 120 seconds.

Please refer to Figure 5. Low heat transfer heating by hot stamping of the present invention The forming method of the mold and the hot stamping part, the experimental three sets of test pieces (the first experimental test piece T1, the second experimental test piece T2, the third experimental test piece T3), and the continuous cooling curve is the first in FIG. 5 respectively. The continuous cooling curve t1 of the experimental test piece T1, the continuous cooling curve t2 of the second experimental test piece T2, and the continuous cooling curve t3 of the third experimental test piece T3. In the continuous cooling graph of Fig. 5, the person indicating the M region is the iron phase of the Matian, the iron phase of the Wo period is indicated in the area A, the ferrite phase is indicated in the F area, and the Borne iron phase is indicated in the P area. The area marked with B is a toughened iron phase, and the value in the circle below each curve is the hardness value, and the unit is Mpa.

In Fig. 5, the lower left side of the standard curve C of the black dotted line at the cooling rate of 25 ° C / sec. is the complete 麻田散铁, the metallographic strength is high, and in the right side of the standard curve C, various metal phases are mixed, The strength is softened. In the figure, the continuous cooling curve t1 of the first experimental test piece T1 is combined with different softening means: the moving time of the heating mold 1 moved into the low heat transfer is 10 seconds, the temperature of the heating mold 1 is quenched at 75 ° C for 20 seconds, and the air is cooled for 120 seconds.

The continuous cooling curve t2 of the second experimental test piece T2 was combined with different softening means: the moving time of the heating mold 1 moved into the low heat transfer was 10 seconds, the temperature of the heating mold 1 was quenched at 450 ° C for 100 seconds, and the air was cooled for 120 seconds.

The continuous cooling curve t3 of the third experimental test piece T3 is combined with different softening means: the moving time of the heating mold 1 moved into the low heat transfer is 10 seconds, the temperature of the low heat transfer heating mold 1 is quenched at 450 ° C for 100 seconds, and the air is cooled for 120 seconds.

It can be seen from the above experimental test pieces and FIG. 5 that the first experimental test piece T1 uses a conventional heating mold, so that the cooling curve t1 with the conventional hot stamping can generate a large amount of granulated iron to improve the strength of the product; The cooling curve t2 of the stamping die heating can avoid the formation of the granulated iron to produce a metallurgical structure mainly of toughened iron to reduce the product strength; and the method of the invention combines the low heat transfer of the low heat transfer layer 13 The heating mold 1 and the heating mold 1 for heating the low heat transfer, during the cooling process, the cooling curve t3 even avoids the formation region of most of the toughening iron, and obtains the metallographic structure mainly composed of ferrite iron. , get lower product strength. As can be seen from Figure 5, The hardness of the workpiece under the typical hot stamping process is up to HV446, and the tensile strength is about 1470MPa. The hardness of the workpiece after combining the low heat transfer coating (ceramic coating) and heating the low heat transfer mold mechanism is HV179, about tensile strength. 580 MPa.

The embodiments or examples of the technical means adopted by the present invention are not intended to limit the scope of implementation of the present patent. That is, the equivalent changes and modifications made in accordance with the scope of the patent application of the present invention or the scope of the invention are covered by the scope of the invention.

Claims (9)

A low-heat-transfer heating mold for hot stamping, the structure comprising: a die and a punch molded by a plurality of die faces corresponding to each other, the concave die having a first working area contacting the blank, the convex die having a contact embryo a second working area of the material; and a low heat transfer coating layer covering the first working area and/or the second working area, the low heat transfer plating layer being a ceramic plating layer. The hot stamping low heat transfer heating mold of claim 1, wherein the low heat transfer coating is applied to all or part of the first working area and/or the second working area. A low heat transfer heating mold for hot stamping as described in claim 1, wherein the low heat transfer layer has a thickness of 0.3 mm, a melting point of about 2000 ° C, and a heat transfer coefficient of 2.2 to 2.9 (W/mK). The coefficient of thermal expansion is 11x10 ^-6 (1/K). The hot stamping forming low heat transfer heating mold according to claim 1, wherein the low heat transfer layer is plated in the first working area and/or the plasma spray method. Two working areas. The hot stamping forming low heat transfer heating mold according to claim 4, wherein the surface of the first working area and/or the second working area is roughened before the low heat transfer layer is plated. . A method for forming a hot stamping part, the method comprising: providing a low heat transfer heating mold according to any one of claims 1 to 5; moving a formed steel sheet uniformly heated to a rolling temperature of Austin to the low heat The heated mold is subjected to hot stamping; the formed steel sheet is heated in the low heat transfer mold and the low heat transfer heating mold is subjected to in-mold quenching at a cooling rate of less than 25 ° C / sec. The method for forming a hot stamping part according to claim 6, wherein after the quenching process in the heating mold of the low heat transfer is completed, the step of removing the formed steel sheet from the low heat transfer is further included. The mold is cooled in air for 120 seconds. The method for forming a hot stamping part according to claim 6, wherein the low heat transfer heating mold has a temperature greater than 420 ° C and a quenching time greater than 80 seconds. The method for forming a hot stamping part according to claim 6, wherein the moving time of the formed steel sheet to the low heat transfer heating mold is 10 seconds, and the heating temperature of the low heat transfer heating mold is 450 ° C. The quenching time was 100 seconds and the air cooling time was 120 seconds.